Gearvendors length

[Greg72]

The 700 R4 had different ratios OD available. 0.86:1 was used also. Therefore 3.08 x 0.86 = 2.65 effective axle ratio. With 29" tires the factory probably expected acceptable customer satisfaction.
15 years ago I read in some OEM technical journal that a 2.70:1 axle ratio is the lowest neumeric ratio that that a V8 engine would pull. Please bear in mind a smaller (lighter) more aerodinamic body powered by a V6 ( torque range 1200 - 1800rpm ) probably could handle a lower 2.54:1 ratio.
A Suburban or Blazer is heavy, not aerodinamic, and is designed to haul loads. GM would not risk its reputation on a less than adequate truck.
The ideal truck for highway use should have a 3.08 - 3.23 axle. This truck should get resonable fuel economy and still haul the freight. This is my opinion.

I remember reading somewhere (probably a LONG time ago) of a way to calculate the amount of HP required to keep a vehicle moving at highway speed. From what I remember it was some sort of procedure where you brought the vehicle up to speed and then let it "coast down" to a lower speed and measured the number of seconds it took.

This factored in aerodynamic drag, rolling resistance, and driveline losses...and was most accurate because the calculations were based on your actual vehicle.

If you knew, for example, that it takes 110HP to push a heavy truck through the air at 70MPH....then you can apply all of these other gearing considerations against that value to see if you will have a "surplus" of power...or if you'll be struggling to stay at your chosen speed.



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[dyeager535]

There are actual GM numbers out there for these trucks, how much power it takes to keep it moving. I think it may have even been posted here.

Obviously it isn't going to cover all drivetrain combos, but it's at least going to be close based on weight and overall aerodynamics.

 

[77crewcab]

No rush, just want some confirmation on the length measured from the back of the t-case. Some pics would be cool too if you can get them just to see what it looks like all together.

 

[77crewcab]

That would be cool information to have. I am thinking that the combo I am looking at will be more than addequate to make me happy. Like I said my daily driver burb is 3.42 on 31s. Sure it could use a little more power but I also realize it is a big heavy vehicle, with an worn engine that was probably on the weakside from the factory, but it does the job with no real problems. If I can setup the new chasis with an effective ratio that is slightly higher than what I have now, with more hp/tq at the cruise level than what my engine has max now, then I am doing great. BTW one thing I haven't said yet is that while I am using a burb chasis the body will actually be a 62 chevy pickup with a custom built 9-10ft (to fit the frame) fleetside bed. It should actually be a little lighter than the burb which will help out as well.

 

[dyeager535]

I thought I'd seen it somewhere.

http://coloradok5.com/forums/showthread.php?t=113688&highlight=coefficient+of+drag